Papers by Author: Chuan Li

Abstract: Small current grounding power system is widely used in overhead transmission line in medium voltage distribution network in China. Because of its long lines, branch, space truss structure is complex, low level of automation, It is easily influenced by outside force and the natural environment, and single-phase grounding failure rate is high. It is an important topic to quickly and accurately detect the location of the fault line, and improve the reliability of power supply and distribution system.This paper has carried on the induction and the comparison of various fault detection and location method of overhead transmission line which is currently used in single phase to ground, and analyzed their advantages and disadvantages,given the corresponding conclusions, provided the reference for finding out the reasonable single-phase earth fault location method or improvement.

Abstract: Safety of secondary lining is of utmost importance to tunnel engineering quality as the main load-bearing structure and the last waterproof line of rock tunnel under type III. The comparative study of strain state results from FEM numerical simulation and on-site monitoring in Yunnan Tianxin Tunnel was conducted to obtain the stress regularity of tunnel lining. The results showed that except vault, the strain states of secondary lining obtained by numerical simulation and on-site monitoring were consistent. The strain value of on-site monitoring was approximately 60%~70% to the simulation value. And the strain value of right side was greater than the value of the corresponding location on the left side. It’s noticed that high strain were found in tunnel haunch and arch springing. Great attention should be paid to arch springing for the largest strain value. The strain monitoring value of vault (309.83με~327.23με) has been detected larger than simulation value (209.37με), which matches well the crack phenomenon of vault. Therefore it’s significant to focus on the long-term monitoring of vault. The defects of single on-site monitoring method such as poor predictability were made up effectively by comparative study. The results achieved can be recommended for similar projects.

Abstract: Seepage pressure is the pressure of pore fluid inside soil, which directly influences the stability state of engineering structure. A differential fiber Bragg grating seepage pressure sensor is developed, in which two fiber Bragg gratings are respectively pasted on the top and bottom surfaces of the uniform intensity cantilever. Acted as the seepage pressure measurement cavity, the free end of metal bellows is connected to the cantilever girder free end. Under the pressure of pore fluid function, the engender axial displacement of metal bellows is converted to the deflection change of cantilever girder free end, which generates the wavelength shifts of two pasted fiber Bragg gratings. The experiment results of pressure loading and unloading show that the sensitivity of the sensor is 1.96 nm/ MPa, the repeatability error is 2.27% FS, and the nonlinear error is 1.7% FS.

Abstract: During the period of tunnel excavation, shoring, forming and long-term operation, stress changes of tunnel surrounding rock are complex, the real-time monitoring of surrounding rock pressure is the key factor in ensuring long-term stability in tunnel. Fiber Bragg grating earth pressure sensors apply in surrounding rock pressure of tunnel which can change the pressure of the surrounding rock into fiber Bragg grating wavelength shift. According to the feature of pressure and temperature in Tian Xin Tunnel, 40 earth pressure sensors are embedded in 20 representative sections and one earth pressure sensor is embedded in each arch shoulder. In addition, one temperature compensation sensor is embedded in each arch crown. During the 235 monitoring days, the biggest daily change of surrounding rock pressure reaches 800 KPa. In 3 months of the sensor installation, the average monthly variation is within 50 KPa. The long-term measurement results indicate that the changes of surrounding rock pressure are different in different locations. When the surrounding rock is close to the excavated and blasted surface the surrounding rock pressure changes largely.

Abstract: Concrete embedded fiber Bragg grating strain sensors are used to monitor real-time strain of each section in the tunnel surrounding rock supporting structure, and the nonlinear regression analysis method is adopted to analysis the real-time measurement data. By using nonlinear regression analysis method, the strain development status of surrounding rock supporting structure can be grasped timely and the variation trend of the strain value of monitoring point can be predicted, which can provides foundations for judging the stability of tunnel supporting structure.

Abstract: When porcelain insulator operates in a harsh environment for a long time, it will cause leakage current increase, and lead to heating phenomenon. As a result, the temperature of porcelain insulator can be changed, which probably due to crack, breakdown or other factors. In order to reflect the working state of the porcelain insulator, to monitor the temperature of porcelain insulator, optical fiber Bragg grating temperature sensors are installed respectively on the steel cap and the porcelain of porcelain insulator. In the interaction of industrial frequency voltage test of 15kV, thus the temperature of porcelain insulator can be distributed. The temperature of the porcelain insulator affects the center wavelength of optical fiber Bragg grating temperature sensors, which are installed on porcelain insulator. The tests show that in the pure condition, the temperature of porcelain insulator's steel cap and porcelain respectively rise 1.4°C and 1.5°C, in the polluted condition, the temperature of porcelain insulator's steel cap and porcelain respectively rise 5.8°C and 6.3°C, in the pollution level II condition, the temperature of Porcelain insulator's steel cap and porcelain respectively rise 6.8°C and 7.2°C. Therefore, by using optical fiber Bragg grating temperature sensors to monitor the change of porcelain insulator's temperature, combined with the researches of temperature characteristics, can directly reflect the porcelain insulator's working situation and real-time online monitoring.

Abstract: Under the influence of ice coating and other natural factors, Power tower cross arm will deform, damage and even fracture with the increasing stress. On the power tower of Yanjin converting station, four fiber Bragg grating strain sensors were installed. By changing the internal force that main material of the cross arm suffered, deflection change of each main material occurred, resulting in fiber Bragg grating wavelength of the fiber Bragg grating strain sensors which on the surface of the cross arm shifting. During the 479 days monitoring, the # 2 sensor daily mean strain range is the largest with the value of 1700.98, while the 3 # sensors have the smallest value of 1122.91. On the July 20th 2011, daily mean strain of the 2# strain sensor located in the insulation cross arm reached the maximum value 382.01, while on the February 19th 2011, that of the 4# sensor achieved the minimum value -1477.75.On the February 19th 2011, both local wind direction and speed had the biggest changes through the testing process, which indicates that the cable sweeping wind is the mainly reason to cause the power tower cross arm deformation.

Abstract: The polytetrafluoroethylene (PTFE) with the good dielectric property is a kind of nonpolar material. Made from the PTFE, the cannula has the high electrical insulation performance. This cannula can be applied to the equipment which requires for the high electrical insulation. There are 3 kinds of power-frequency voltage resistant experiments on PTFE cannulas with the inner diameter and outer diameter of 0.55/1.35, 0.7/1.5, 0.96/1.6, 0.46/0.96, 1.5/3.0 in the 1970m elevation. The PTFE cannulas are tested at the 85kV power-frequency voltage with the pure condition, the humidity condition, and the polluted condition separately in 1 minute. The result induced that the PTFE cannula did not be destroyed in all of the above experiments with no puncture sound, no smoke, no flashover and no burning. The insulating quality of the PTFE cannula is satisfied with the insulation requirement of the 85kV, i.e., the pollution level I.

Abstract: In long-period running of switch cabinet, the temperature of contact points will be rose by the big contact resistance, poor contact and longtime overloading. Overheat can cause oxidation of contact points and the increasing of contact resistance, and then the contact may be generated the spark and arc discharge. That is a bad circle. So the temperature of contact points can affect the reliability of switch cabinet. For detecting the temperature of contacts and the switch cabinet’s environment in Yanjin transformer substation, we design an Insulated FBG temperature sensor. The surveys of upper reaches indicate that the temperature of moving contact A gets the maximum 32.98°C Aug.20, 2011, the temperature of stationary contact A gets the minimum 5.75°C, and the change temperature between contacts and environment gets the maximum 2.82°C. According to relevant state regulations, the contact’s temperature of 70 °C and temperature’s changes of 35 °C in the case of environment’s temperature below 40°C are Alarm threshold value of switch cabinet.

Abstract: Silicone rubber is a polymer with the chain molecule structure of Si-O bond [1]. At the environment of 1970 m elevation, the power frequency withstand voltage and condensation experiments will be tested by using two silicone rubber tubes with length of 300mm and 330mm, which lasts one minute, under 85kV. In the high potential test, the silicone rubber tube does not appear the flashover when the surface of tubes weren’t polluted. However, the test voltage increases to 70kV and the surface of the silicone rubber tube will appear flashover, when the tubes are plated in the condensation conditions. The high potential experiments indicate that the electrical insulation property of silicone rubber tube is seriously debated in the humidity environment.